Lipoprotein-associated phospholipase A2 (Lp-PLA2) previously known as platelet-activating factor acetylhydrolase (PAF-AH), is a phospholipase A2 enzyme involved in hydrolysis of lipoprotein lipids or phospholipids. Lp-PLA2 travels with low-density lipoprotein (LDL) and rapidly cleaves oxidized phosphatidylcholine molecules derived from the oxidation of LDL. (See e.g., Zalewski A, et al., Arterioscler. Thromb. Vasc. Biol., 25, 5, 923-31(2005)). Lp-PLA2 hydrolyzes the sn-2 ester of the oxidized phosphatidylcholines to give lipid mediators, lyso-phosphatidylcholine (lysoPC) and oxidized nonesterified fatty acids (NEFAs). It has been observed that lysoPC and NEFAs elicit inflammatory responses. (See e.g., Zalewski A, et al. (2005)).
A number of Lp-PLA2 inhibitors and/or uses thereof have been previously described. (See. for example, published patent application nos. WO96/13484, WO96/19451, WO97/02242, WO97/12963, WO97/21675, WO97/21676, WO 97/41098, WO97/41099, WO99/24420, WO00/10980, WO00/66566, WO00/66567, WO00/68208, WO01/60805, WO02/30904, WO02/30911, WO03/015786, WO03/016287, WO03/041712, WO03/042179, WO03/042206, WO03/042218, WO03/086400, WO03/87088, WO08/048867, US 2008/0103156, US 2008/0090851, US 2008/0090852, and WO08/048866.) Disclosed uses include treating disease that involves or is associated with endothelial dysfunction, disease that involves lipid oxidation in conjunction with Lp-PLA2 activity (e.g., associated with the formation of lysophosphatidylcholine and oxidized free fatty acids), and disease that involves activated monocytes, macrophages or lymphocytes or which is associated with increased involvement of monocytes, macrophages or lymphocytes. Examples of diseases include atherosclerosis (e.g. peripheral vascular atherosclerosis and cerebrovascular atherosclerosis), diabetes, hypertension, angina pectoris, after ischaemia and reperfusion, rheumatoid arthritis, stroke, inflammatory conditions of the brain such as Alzheimer's disease, various neuropsychiatric disease such as schizophrenia, myocardial infarction, ischaemia, reperfusion injury, sepsis, acute and chronic inflammation, and psoriasis.
Lp-PLA2 inhibitors and/or uses thereof are also reported, for example, in PCT Publication Nos. WO05/003118 (and its Canadian family member CA 2530816A1); WO06/063811; WO06/063813 and WO 2008/141176; JP 200188847; and US Published Patent Application Nos. US 2008/0279846 Al, US 2010/0239565 A1, and US 2008/0280829 A1.
Other researchers have studied the effects related to Lp-PLA2 and inhibitors thereof. For example, research data has also indicated that LysoPC promotes atherosclerotic plaque development, which can ultimately lead to the formation of a necrotic core. (See e.g., Wilensky et al., Current Opinion in Lipidology, 20, 415-420 (2009)). In addition, the effect of Lp-PLA2 inhibitors on atherosclerotic plaque composition was demonstrated in a diabetic and hypercholesterolemic porcine model of accelerated coronary atherosclerosis. (See e.g., Wilensky et al., Nature Medicine, 10, 1015-1016 (2008)). These research results provided further evidence that Lp-PLA2 inhibitors may be used to treat atherosclerosis.
Additional studies indicate that high Lp-PLA2 activity is associated with high risk of dementia, including Alzheimer's disease (AD) (See e.g., Van Oijen, et al. Annals of Neurology, 59,139 (2006)). Higher levels of oxidized LDL have also been observed in AD patients (See e.g., Kassner et al. Current Alzheimer Research, 5, 358-366 (2008); Dildar, et al., Alzheimer Dis Assoc Disord, 24, April-June (2010); Sinem, et al. Current Alzheimer Research, 7, 463-469 (2010)). Further, studies show that neuroinflammation is present in AD patients and multiple cytotoxic inflammatory cytokines are up-regulated in AD patients. (See e.g., Colangelo, et al., Journal of Neuroscience Research, 70, 462-473 (2002); Wyss-Coray, Nature Medicine, 12, Sept. (2006)). Research has shown that LysoPC function is a pro-inflammatory factor inducing multiple cytotoxic inflammatory cytokine release (See Shi, et al. Atherosclerosis, 191, 54-62 (2007)). Therefore, these studies provide additional evidence that that the inhibitors of Lp-PLA2 can be used to treat AD by inhibiting activity of Lp-PLA2 and reducing lysoPC production.
In addition, use of an Lp-PLA2 inhibitor in a diabetic and hypercholesterolemia swine model demonstrated that blood-brain-barrier leakage and brain amyloid beta protein (Aβ) burden, the pathological hallmarks of Alzheimer's disease, were reduced. (See U.S. Patent Application Publication No. 2008/0279846). This publication describes several uses of Lp-PLA2 inhibitors for treating diseases associated with blood-brain-barrier leakage, including, e.g., Alzheimer's disease and vascular dementia.
Further, neuroinflammation, including multiple cytotoxic cytokine release, is a common feature of all neurodegenerative diseases including multiple sclerosis, amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, etc. (See e.g., Perry, Acta Neuropathol, 120, 277-286 (2010)). As discussed above, Lp-PLA2 inhibitors can reduce inflammation, for example, reducing multiple cytokine release by suppressing lysoPC production. (See e.g., Shi, et al. Atherosclerosis 191, 54-62 (2007)). Thus, inhibiting Lp-PLA2 is a potential therapeutic treatment for neurodegenerative diseases including multiple sclerosis, amyotrophic lateral sclerosis, Parkinson's disease, etc.
In addition to the inflammatory effect, LysoPC has been implicated in leukocyte activation, induction of apoptosis and mediation of endothelial dysfunction (See, e.g., Wilensky et al., Current Opinion in Lipidology, 20, 415-420 (2009)). Therefore, it is believed that Lp-PLA2 inhibitors can be used to treat tissue damage associated with diabetes by reducing the production of lysoPC, which can cause a continuous cycle of vascular inflammation and increased reactive oxygen species (ROS) production. In light of the inflammatory roles of Lp-PLA2 and the association between localized inflammatory processes and diabetic retinopathy, it is postulated that Lp-PLA2 can be used to treat diabetic ocular disease.
Glaucoma and age-related macular degeneration (AMD) are retina neurodegenerative diseases. Studies suggest that inflammation, including TNF-alpha signaling, may play an important role in the pathogenesis of glaucoma and AMD (See e.g., Buschini et al., Progress in Neurobiology, 95, 14-25 (2011); Tezel, Progress in Brain Research, vol. 173, ISSN0079-6123, Chapter 28). Thus, considering Lp-PLA2 inhibitors' function of blocking inflammatory cytokine release (See e.g., Shi, et al. Atherosclerosis, 191, 54-62 (2007)), it is believed that Lp-PLA2 inhibitors can provide a potential therapeutic application for both glaucoma and AMD.
In view of the number of pathological responses that are mediated by Lp-PLA2, attempts have been made to prepare compounds that inhibit its activity. Though a number of such compounds have been disclosed in the art, there remains a continuing need for inhibitors of Lp-PLA2 which can be used in the treatment of a variety of conditions.